This invention relates to large cooling towers and more specifically to improved air distribution within a large counter-flow cooling tower.
Cooling towers function to exchange heat from water to air and usually are denominated as parallel flow, cross flow or counter-flow according to the relative flow of air and water. The heat exchange may occur by simply passing air past a stream of water. However since the exchange takes place at the water surface it is advantageous to maximize the water surface per unit volume of water. Normally this is done by breaking the water flow into small droplets or spreading the water flow across multiple sheets of fill material, and in the latter instance the air is moved between the fill sheets. The usual cooling tower thus contains banks of closely spaced fill sheets arranged vertically with an overhead warm water distribution network and a cooled water collection pool beneath the fill sheets. Air is moved between the sheets to thereby cool the downwardly flowing water by both conduction and evaporation. The air will be drawn from outside the tower, moved upwardly in a counter-flow cooling tower, and its cooling capacity will be used and reduced as it moves past the water surface toward the warm water source.
It is notable that the fill sheet material is often manufactured of a flammable material and it is possible, particularly during periods that water flow may be terminated, diverted or diminished, for combustion to occur within the fill of a cooling tower. Thus it would be advantageous to devise means to limit the opportunity for combustion to initiate and/or to spread within the fill in a cooling tower.
Cooling towers are constructed in an extremely wide range of sizes extending from small commercial units only a few feet high and wide to enormous industrial units measuring in the hundreds of feet. For example hyperbolic cooling towers measuring 400 feet in diameter, at the base, and 500 feet high have been constructed for the nuclear power industry to induce upward air drafts sufficient to cool water at rates in excess of a half million gallons per minute. Nevertheless those enormous units and the small units function in essentially the above described manner.
In counter-flow cooling towers the ambient air is shielded from the sides of the fill and is permitted entrance from only the underside so that it crosses the full vertical dimension of the fill sheets. The physical structure of most counter-flow cooling towers usually requires that the unit rest upon the earth or some building so as to require ambient air to enter horizontally at the bottom of the unit beneath the fill sheets, usually from about the perimeter or circumference thereof, and turn upwardly within the tower unit. It has been found that as a result relatively larger quantities of the upwardly moving air will become concentrated at the outer portions of the fill sheets while the interior portions will become relatively starved for air and the heat exchange becomes inefficient in the center of the unit. It follows that as the horizontal dimensions of a counterflow cooling tower become larger there will be an ever greater portion and quantity of internally located fill sheet surface that will be relatively starved for air and thus a substantial loss of real cooling capacity will occur.
Moreover the usual cooling tower structure includes a sump-pan, pool or reservoir at the bottom to receive the cooled water that falls from the bottom of the fill sheets. The ambient air flow must enter horizontally between the sump and the bottom of the fill sheets through a space that is filled with free falling droplets and streams of water which not only physically impede horizontal air movement but also begin to warm and saturate the air before it reaches the centrally located fill sheets. Thus it has been found that as the distance increases through which an increment of ambient air must move horizontally through free falling water the increment of air encounters increasing flow resistance and suffers a loss in its capacity to absorb additional heat; and the air that heretofore has reached the internal portion of large dimension cooling towers has been reduced in velocity and quantity and has had significantly diminished cooling capacity. Thus it would be advantageous to devise a means to introduce fresh ambient air to the internal portions of a cooling tower without having to pass first through an area of freely falling water.
Our recognition of the significance of these factors tending to reduce the effectiveness of the internal portions of large cooling towers, especially the enormous hyperbolic towers, has enabled us to devise structural features that overcome the problems and deliver fresh ambient air to the internal portions of the fill. The same structural features also serve to segregate adjacent areas of fill against spread of combustion.